Solid state imaging device and fabrication method for the same

ABSTRACT

A solid state imaging device with an easy structure in which have the high sensitivity which reaches the wide wavelength region from visible light to near infrared light wavelength region, and dark current is reduced, and a fabrication method for the same, are provided. 
     A solid state imaging device and a fabrication method for the same, the solid state imaging device comprising: a circuit unit formed on a substrate; and a photoelectric conversion unit including a lower electrode layer placed on the circuit unit, a compound semiconductor thin film of chalcopyrite structure which is placed on the lower electrode layer and functions as an optical absorption layer, and an optical transparent electrode layer placed on the compound semiconductor thin film, wherein the lower electrode layer, the compound semiconductor thin film, and the optical transparent electrode layer are laminated one after another on the circuit unit.

TECHNICAL FIELD

The present invention relates to a solid state imaging device and afabrication method for the same. In particular, the present inventionrelates to a solid state imaging device provided with a compoundsemiconductor film of a chalcopyrite structure composed of Cu(In, Ga)Se₂in a photoelectric conversion unit, and a fabrication method for thesame.

BACKGROUND ART

The thin film solar cell using CuInSe₂ (CIS based thin film) which isthe semiconductor thin film of chalcopyrite structure composed of agroup Ib element, a group IIIb element, and a group IVb element, orCu(In, Ga)Se₂ (CIGS based thin film) which dissolves Ga to this, for anoptical absorption layer, has an advantage that high energy conversionefficiency is indicated and there is little degradation of theefficiency according to light irradiation etc.

However, film formation by 550 degrees C. from a viewpoint ofdeterioration of film quality and increase of leakage current isgeneral, in formation of the CIS based thin film which is thesemiconductor thin film of chalcopyrite structure, or the CIGS basedthin film which dissolves Ga to this. When it forms at low temperaturerather than 550 degrees C., it has been considered that particlediameter is small composed and dark current characteristics deteriorate,conventionally. In addition, the heat-resistant limitation of anintegrated circuit is about 400 degrees C.

On the other hand, a solid state imaging element characterized byforming a switching device by a thin film transistor on a substrate andlaminating a sensor area by an amorphous semiconductor layer via apicture element electrode connected to the above-mentioned switchingdevice or a solid state imaging element with which the above-mentionedsubstrate is formed by an insulating substrate is already disclosed (forexample, refer to Patent Literature 1).

In the solid state imaging element disclosed in Patent Literature 1,since the amorphous semiconductor layer is made into a photo sensorarea, a photoelectric conversion wavelength is mainly a visible lightwavelength region.

Patent Literature 1: Japanese Patent Application Laying-Open PublishingNo. 2001-144279

Currently, the CIS based thin film and the CIGS based thin film have themain use as a solar battery.

On the other hand, the inventors of the present invention have paidtheir attention to a high optical absorption coefficient of thiscompound semiconductor thin film material and characteristics with thehigh sensitivity which reaches the wide wavelength region from visiblelight to near infrared light wavelength region, and have examined usingthis compound semiconductor thin film material as an image sensor for asecurity camera (camera which performs sensing of the visible light atdaytime and performs sensing of the near infrared light wavelengthregion at night), a personal authentication camera (camera forperforming personal authentication with the near infrared lightwavelength region which is not affected by an influence of outdoordaylight) or an in-vehicle camera (camera mounted in a car for visualaid at night, distant visual field securing, etc.).

An object of the present invention is to provide a solid state imagingdevice, with an easy structure, having the high sensitivity whichreaches the wide wavelength region from visible light to near infraredlight wavelength region and reducing dark current by providing aphotoelectric conversion unit with a compound semiconductor film of thechalcopyrite structure composed of Cu(In, Ga)Se₂ in the photoelectricconversion unit.

Moreover, an object of the present invention is to provide a fabricationmethod of the above-mentioned solid state imaging device.

DISCLOSURE OF INVENTION

A solid state imaging device of the present invention for achieving theabove-mentioned object comprises: a circuit unit formed on a substrate;and a photoelectric conversion unit including a lower electrode layerplaced on the circuit unit, a compound semiconductor thin film ofchalcopyrite structure which is placed on the lower electrode layer andfunctions as an optical absorption layer, and an optical transparentelectrode layer placed on the compound semiconductor thin film, whereinthe lower electrode layer, the compound semiconductor thin film, and theoptical transparent electrode layer are laminated one after another onthe circuit unit.

According to this configuration, the solid state imaging device, with aneasy structure, having the optical absorption sensitivity of thecompound semiconductor thin film of chalcopyrite structure can beobtained.

In the solid state imaging device of the present invention, the circuitunit includes a transistor by which the lower electrode layer isconnected to a gate.

According to this configuration, the solid state imaging device which isprovided with the optical absorption sensitivity of the compoundsemiconductor thin film of chalcopyrite structure, and is provided withthe amplifying function by a transistor can be obtained.

In the solid state imaging device of the present invention, the circuitunit includes a transistor by which the lower electrode layer isconnected to a source or a drain.

According to this configuration, the solid state imaging device which isprovided with the optical absorption sensitivity of the compoundsemiconductor thin film of chalcopyrite structure and whose opticalaperture improved can be obtained.

In the solid state imaging device of the present invention, the circuitunit and the photoelectric conversion cell composed of the photoelectricconversion unit are integrated.

According to this configuration, the solid state imaging devicesprovided with the optical absorption sensitivity of the compoundsemiconductor thin film of chalcopyrite structure, such as a line sensorand an area sensor, can be provided.

In the solid state imaging device of the present invention, the circuitunit and the photoelectric conversion cell composed of the photoelectricconversion unit are integrated, and the optical transparent electrodelayer is formed on a substrate surface in one piece.

According to this configuration, the solid state imaging device, with aneasy structure, in which provides the optical absorption sensitivity ofthe compound semiconductor thin film of chalcopyrite structure, andwhich does not need patterning the optical transparent electrode layercan be obtained.

In the solid state imaging device of the present invention, the compoundsemiconductor thin film of the chalcopyrite structure is Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1).

According to this configuration, the widening of bandgap energy of theCIS based thin film (CuInSe₂) becomes effective by using the CIGS basedthin film which displaced a part of In (indium) to gallium. Accordingly,by expanding the bandwidth, the recombination processing of carriers canbe reduced and reduction of dark current can be achieved.

In the solid state imaging device of the present invention, the opticaltransparent electrode layer includes a non-doped ZnO film provided on aninterface with the compound semiconductor thin film, and an n type ZnOfilm provided on the non-doped ZnO film.

According to this configuration, the void and the pinhole which areproduced in the CIGS thin film of the underlying are embedded by asemi-insulating layer by providing a non-doped ZnO film (i-ZnO) as theoptical transparent electrode layer, and the generation of leakagecurrent can be prevented.

Therefore, the dark current at the pn junction interface can be reducedby forming the non-doped ZnO film (i-ZnO) as a thick film.

The solid state imaging device of the present invention is a photosensor having sensitivity also in a near infrared optical wavelengthregion.

Since the solid state imaging device of the present invention has highsensitivity also in a near infrared light wavelength region, the solidstate imaging device is available enough as an image sensor for asecurity camera (camera which performs sensing of the visible light atdaytime and performs sensing of the near infrared light wavelengthregion at night), and personal authentication camera (camera forperforming personal authentication with the near infrared lightwavelength region which is not affected by an influence of outdoordaylight) or in-vehicle camera (camera mounted in a car for visual aidat night, distant visual field securing, etc.).

The solid state imaging device of the present invention includes a colorfilter on the optical transparent electrode layer.

According to this configuration, the image sensor for colors can beprovided in the visible light wavelength region.

A fabrication method of a solid state imaging device of the presentinvention in which a circuit unit on a substrate, a lower electrodelayer, a compound semiconductor thin film of chalcopyrite structure thatfunctions as an optical absorption layer, and an optical transparentelectrode layer are laminated to be composed. The fabrication methodcomprises: forming the circuit unit on the substrate; forming the lowerelectrode layer on the substrate on which the circuit unit is formed;patterning the lower electrode layer by photo lithography, andseparating for every pixel, forming the compound semiconductor thin filmof the chalcopyrite structure all over an element region; and patterningthe compound semiconductor thin film of the chalcopyrite structure byphoto lithography, and separating for every pixel according to theseparated underlying lower electrode layer.

The fabrication method of the solid state imaging device of the presentinvention further comprises: depositing an interlayer insulating filmall over the element region; and patterning the interlayer insulatingfilm by photo lithography, and exposing the compound semiconductor thinfilm surface of the chalcopyrite structure for every pixel.

The fabrication method of the solid state imaging device of the presentinvention further comprises forming the optical transparent electrodelayer all over the element region.

The fabrication method of the solid state imaging device of the presentinvention further comprises forming a buffer layer all over the elementregion after the step of exposing the compound semiconductor thin filmsurface.

In the fabrication method of the solid state imaging device of thepresent invention, the step of forming the compound semiconductor thinfilm of the chalcopyrite structure includes the step of formingCu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1) thin film by PVD.

The fabrication method of the solid state imaging device of the presentinvention further comprises forming a color filter on the opticaltransparent electrode layer.

In the fabrication method of the solid state imaging device of thepresent invention, the step of forming the optical transparent electrodelayer includes: forming a non-doped ZnO film; and forming an opticaltransparent electrode film, such as an n type ZnO film and an ITO film,on the non-doped ZnO film.

In the fabrication method of the solid state imaging device of thepresent invention, the step of forming the compound semiconductor thinfilm of the chalcopyrite structure includes: the first step ofpatterning by dry etching; and the second step of removing an etchingresidue produced at the first step by wet etching.

In the fabrication method of the solid state imaging device of thepresent invention, the first step uses chlorine series gas and bromineseries gas as etchant to perform dry etching, and the second step isprocessed with hydrochloric acid in order to remove a compound of Cuwhich remains at the first step.

In the fabrication method of the solid state imaging device of thepresent invention, the compound semiconductor thin film of thechalcopyrite structure is Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1).

The fabricated solid state imaging device according to the presentinvention fabricated by the fabrication method of the solid stateimaging device according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] It is a whole schematic plane pattern configuration diagram ofa solid state imaging device according to a first embodiment of thepresent invention.

[FIG. 2] It is a schematic cross-sectional configuration diagram of thesolid state imaging device according to the first embodiment of thepresent invention.

[FIG. 3] It is a schematic cross-sectional configuration diagramincluding adjoining pixels of the solid state imaging device accordingto the first embodiment of the present invention

[FIG. 4] A processing diagram of a fabrication method of the solid stateimaging device according to the first embodiment of the presentinvention,

-   (a) a sputtering process diagram of a lower electrode layer (Mo),-   (b) an etching process diagram of a lower electrode layer (Mo)-   (c) a formation process diagram of a compound semiconductor thin    film (CIGS thin film) of chalcopyrite structure which functions as    an optical absorption layer,-   (d) an etching process diagram of the compound semiconductor thin    film (CIGS thin film),-   (e) a deposition process diagram of an interlayer insulating film,-   (f) an etching process diagram of the interlayer insulating film,-   (g) a solution growth processing diagram of a buffer layer (CdS    film), and-   (h) a sputtering process diagram of an optical transparent electrode    layer (ZnO film).

[FIG. 5] It is a detailed explanation diagram of a formation process ofthe compound semiconductor thin film of the chalcopyrite structureapplied to the solid state imaging device according to the firstembodiment of the present invention.

[FIG. 6] It is an SEM photographic diagram of a cross-section structureof a photoelectric conversion unit formed by the fabrication method ofthe solid state imaging device according to the first embodiment of thepresent invention.

[FIG. 7] A schematic diagram of an energy band structure in thephotoelectric conversion unit of the solid state imaging deviceaccording to the first embodiment of the present invention,

-   (a) a schematic diagram of energy band structure at the time where    the composition of the CIGS thin film is formed uniform,-   (b) a schematic diagram of the energy band structure at the time of    performing bandgap control, and-   (c) a detailed enlarged drawing of the energy band structure of    CIGS (p) thin film 24 part at the time of performing bandgap    control.

[FIG. 8] It is an example of an analysis result by AES (Auger ElectronSpectroscopy) of the compound semiconductor thin film (CIGS thin film)of the photoelectric conversion unit formed by the fabrication method ofthe solid state imaging device according to the first embodiment of thepresent invention, and is a relationship diagram of atomic concentration(%) and a sputtering time.

[FIG. 9] It is a dependence characteristics diagram of the bandgapenergy of the compound semiconductor thin film of chalcopyrite structureand In/(In+Ga) composition ratio which are applied to the solid stateimaging device according to the first embodiment of the presentinvention.

[FIG. 10] It is a wavelength characteristic of quantum efficiency forexplaining the photoelectric conversion characteristic of the solidstate imaging device according to the first embodiment of the presentinvention.

[FIG. 11] It is a wavelength characteristic of the quantum efficiency ofthe compound semiconductor thin film (CIGS thin film) formed by thefabrication method of the solid state imaging device according to thefirst embodiment of the present invention.

[FIG. 12] It is an optical absorption characteristics diagram of thesolid state imaging device according to the first embodiment of thepresent invention.

[FIG. 13] It is a schematic cross-sectional configuration diagram of onepixel part of the solid state imaging device according to a modifiedexample of the first embodiment of the present invention.

[FIG. 14] It is a schematic cross-sectional configuration diagram of asolid state imaging device according to a second embodiment of thepresent invention.

[FIG. 15] It is a schematic cross-sectional configuration diagram of onepixel part of a solid state imaging device according to a modifiedexample of the second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the invention is described with reference todrawings. In the description of the following drawings, the same orsimilar reference numeral is attached to the same or similar part.However, a drawing is schematic and it should care about differing froman actual thing. Drawings are schematic, not actual, and may beinconsistent in between in scale, ratio, etc.

The embodiment shown in the following exemplifies the device and methodfor materializing the technical idea of this invention, and thistechnical idea of the invention does not specify assignment of eachcomponent parts, etc. as the following. Various changes can be added tothe technical idea of this invention in scope of claims.

[First Embodiment]

(Element Structure)

As shown in FIG. 1, a whole schematic plane pattern configuration of asolid state imaging device according to a first embodiment of thepresent invention includes: a package substrate 1; a plurality ofbonding pads 2 placed at the periphery on the package substrate 1; andan aluminum electrode layer 3 which is connected with the bonding pad 2via a bonding pad connecting unit 4, and is connected to a transparentelectrode layer 26, placed on a pixel 5 of the solid state imagingdevice, in the periphery of the solid state imaging device. That is, thealuminum electrode layer 3 covers an end region of the transparentelectrode layer 26, and the aluminum electrode layer 3 is connected tothe one bonding pad 2 via the bonding pad connecting unit 4. Moreover,the pixel 5 is placed at matrix shape in the example of FIG. 1.

As shown in FIG. 2, a schematic cross-section structure of the solidstate imaging device according to the first embodiment of the presentinvention includes a circuit unit 30 formed on a substrate, and aphotoelectric conversion unit 28 placed on the circuit unit 30.

The photoelectric conversion unit 28 includes a compound semiconductorthin film (Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1)) 24 of chalcopyritestructure which functions as an optical absorption layer, and an opticaltransparent electrode layer 26 placed on the compound semiconductor thinfilm 24.

The optical transparent electrode layer 26 is composed of a non-dopedZnO film (i-ZnO) provided on the compound semiconductor thin film 24,and an n⁺ type ZnO film provided on the non-doped ZnO film (i-ZnO).

The circuit unit 30 is formed by a CMOSFET (Complementary Metal OxideSemiconductor Field Effect Transistor) integrated circuit etc., forexample.

In FIG. 2, an n channel MOS transistor which composes a part of the CMOSis shown in the circuit unit 30, and the circuit unit 30 includes: asemiconductor substrate 10; source/drain regions 12 formed in thesemiconductor substrate 10; a gate insulating film 14 placed on thesemiconductor substrate 10 between the source/drain regions 12; a gateelectrode 16 placed on the gate insulating film 14; a VIA0 electrode 17placed on the gate electrode 16; a wiring layer 18 for gates placed onthe VIA0 electrode 17; and a VIA1 electrode 22 placed on the wiringlayer 18.

All of the gate electrode 16, the VIA0 electrode 17, the wiring layer18, and the VIA1 electrode 22 are formed in an interlayer insulatingfilm 20.

A VIA electrode 32 placed on the gate electrode 16 is formed of the VIA0electrode 17, the wiring layer 18 placed on the VIA0 electrode 17, andthe VIA1 electrode 22 placed on the wiring layer 18. The VIA electrode32 is shown also in a cross-section structure of FIG. 3 or FIG. 13described later.

In the solid state imaging device, the gate electrode 16 of the nchannel MOS transistor which composes a part of the CMOS and thephotoelectric conversion unit 28 are electrically connected via the VIAelectrode 32 placed on the gate electrode 16.

Since an anode of a photo diode, which composes the photoelectricconversion unit 28, is connected to the gate electrode 16 of the nchannel MOS transistor, optical information detected in the photo diodeis amplified by the n channel MOS transistor.

In addition, although the circuit unit 30 is shown by the example of thesemiconductor integrated circuit placed on the semiconductor substrate10 in the example of FIG. 2, the circuit unit 30 can also be formed witha thin film transistor integrated circuit which integrates a thin filmtransistor formed on a thin film formed on a glass substrate, forexample.

More detailed cross-section structure including the adjoining pixels ofthe solid state imaging device is expressed as shown in FIG. 3, and thesolid state imaging device includes: the circuit unit 30 formed on thesemiconductor substrate 10, and the photoelectric conversion unit 28placed on the circuit unit 30.

The photoelectric conversion unit 28 includes a lower electrode layer25; the compound semiconductor thin film (Cu(In_(X), Ga_(1−X))Se₂ (where0<=X<=1)) 24 of chalcopyrite structure which is placed on the lowerelectrode layer 25 and functions as an optical absorption layer; abuffer layer 36 placed on the compound semiconductor thin film 24; andthe optical transparent electrode layer 26 placed on the buffer layer36.

The lower electrode layer 25 is connected to the gate electrode 16 ofthe MOS transistor in the circuit unit 30 via the VIA electrode 32.

As clearly from FIG. 3, the compound semiconductor thin film 24 placedon the lower electrode layer 25 and the lower electrode layer 25 isseparated each other via the interlayer insulating film 34 betweenadjoining pixel cells.

Moreover, the buffer layer 36 placed on the compound semiconductor thinfilm 24 is formed in one piece all over the semiconductor substratesurface.

Moreover, the optical transparent electrode layer 26 is formed in onepiece all over a semiconductor substrate surface, and is performed incommon electrically.

According to this configuration, the void and the pinhole which areproduced in the CIGS thin film of the underlying are embedded by asemi-insulating layer by providing a non-doped ZnO film (i-ZnO) as theoptical transparent electrode layer, and the generation of leakagecurrent can be prevented. Therefore, the dark current at the pn junctioninterface can be reduced by forming the non-doped ZnO film (i-ZnO) as athick film. In addition, the lower electrode layer 25 and the bufferlayer 36 which are shown in FIG. 3 omitted illustrating in FIG. 2.

(Fabrication Method)

A fabrication method of the solid state imaging device according to thefirst embodiment of the present invention will be explained using aschematic process diagram showing in FIG. 4.

-   (a) First of all, as shown in FIG. 4( a), a molybdenum (Mo) layer is    formed, for example by sputtering technology etc. as the lower    electrode layer 25 on the circuit units 30, such as a CMOS    integrated circuit formed on the semiconductor substrate. The    thickness of the lower electrode layer 25 is about 0.3 μm, for    example.-   (b) Next, as shown in FIG. 4( b), the lower electrode layer 25    composed of the molybdenum (Mo) layer is patterned, and is separated    by etching for every pixel.-   (c) Next, as shown in FIG. 4( c), the compound semiconductor thin    film (CIGS thin film) 24 of chalcopyrite structure which functions    as an optical absorption layer is formed all over the element    surface. Three steps of sputtering processes as shown in FIG. 5    described later by the spattering process, for example can be used    for the formation process of the compound semiconductor thin film    (CIGS thin film) 24. The thickness of the compound semiconductor    thin film (CIGS thin film) 24 is about 1.0 μm, for example.-   (d) Next, as shown in FIG. 4( d), the compound semiconductor thin    film (CIGS thin film (p⁻)) 24 is patterned by two-step etching using    the dry etching and the wet etching together. Accordingly, the    compound semiconductor thin film (CIGS thin film (p⁻)) 24 separated    electrically is obtained.

In detail, when performing dry etching of the compound semiconductorthin film (CIGS thin film (p⁻)) 24 using a resist pattern, it patternsby etching vertically the compound semiconductor thin film (CIGS thinfilm (p⁻)) 24 using chlorine series gas and bromine series gas asetchant. In this case, although the etching which does not almost haveside etching is possible at a high rate, a plurality of pillar-shapedresidues remain on a plurality of Mo films. The residues are removedcompletely by processing with hydrochloric acid. In the above-mentioneddry etching process, Cu(Br)_(x) is generated by reactive gas, andCu(Br)_(x) is removed by the wet etching processes by hydrochloric acidtreatment.

Thus, the compound semiconductor thin film (CIGS thin film (p⁻)) 24which composes an optical absorption layer can be etched with highprecision at a high rate, without producing undercutting region, byusing chlorine series gas and bromine series gas as etchant of dryetching. Then, the pillar-shaped residues are completely removed byperforming short-time wet etching. Accordingly, it is possible ofpatterning of a highly precise CIGS film, without producing theresidues. In this case, neither damage nor a defect is produced in thecrystal of the CIGS thin film 24, but it is possible of the substantialreduction of the dark current. Next, the resist pattern is removed. Adevice cross section of this state is shown in FIG. 4( d). In addition,in FIG. 4( d), in order that it is easy, the width of the compoundsemiconductor thin film 24 after etching and the width of the lowerelectrode layer 25 are illustrated equally. However, in more details, asshown in FIG. 3, it may set up so that the width of the compoundsemiconductor thin film 24 after etching may be wider than the width ofthe lower electrode layer 25.

(e) Next, as shown in FIG. 4( e), the interlayer insulating film 34 isdeposited all over the element surface. As the interlayer insulatingfilm 34, an insulating film, such as a TEOS (tetraethoxy silane) film, aBPSG film, a CVD oxide film, and a CVD nitride film, or these multilayerfilms can be used, for example(f) Next, as shown in FIG. 4( f), the interlayer insulating film 34 ispatterned and the surface of the compound semiconductor thin film (CIGSthin film (p⁻)) 24 is exposed by etching. The width of the exposedregion is narrower than the width of the compound semiconductor thinfilm 24.(g) Next, as shown in FIG. 4( g), the thin CdS film (about 50 nm) as thebuffer layer (window layer) 36 is formed by a solution growth method.The buffer layer 36 can be formed with sufficient coating filmcharacteristics by the solution growth method.(h) Next, as shown in FIG. 4( h), the optical transparent electrodelayer (ZnO film) 26 is formed by a spattering process. At this time, thebuffer layer 36 reduces the damage to the compound semiconductor thinfilm 24.

The optical transparent electrode layer (ZnO film) 26 is formed byforming continuously the non-doped ZnO film (i-ZnO) and the ZnO (n⁺)film of the low resistivity by which the n type impurity is doped. Inthis case, the thickness of i-ZnO is about 60 nm, and, on the otherhand, the thickness of the ZnO (n⁺) film of low resistivity is about 0.5μm.

A non-doped ZnO film (i-ZnO) embeds the void and the pinhole, which areproduced in the CIGS thin film 24 of the underlying, by thesemi-insulating layer, and plays the role which prevents the generationof leakage current.

Therefore, the dark current of the pn junction interface can be reducedby forming the non-doped ZnO film (i-ZnO) as a thick film. However,although the thick film is formed, since this thickness is thin enough(for example, about 60 nm), it is considered that pn junction is formedsubstantially between the ZnO (n⁺) film of low resistivity, whichfunctions as the optical transparent electrode layer 26, and the CIGSthin film (p⁻).

-   (i) Finally, the process of electrode formation is performed. Since    it is the same as that of the electrode formation process in the    usual CMOS process, the explanation is omitted. In addition, since    the optical transparent electrode layer (ZnO film) 26 becomes    equi-potential, it is not necessary to perform isolation formation    of the optical transparent electrode layer (ZnO film) 26 for every    pixel. However, the electrode composed of aluminum etc. may be    placed to be meshed shaped or stripe shaped on the optical    transparent electrode layer (ZnO film) 26 in a fixed pitch, in the    range which does not have on the optical aperture of a pixel, in the    case of the large capacity area sensor etc. with which specific    resistivity becomes a problem.-   (j) Furthermore, in a visible light wavelength region, when imaging    a color picture, a color filter may be placed on the optical    transparent electrode layer (ZnO film) 26. The color filters may be    provided of a filter for red, a filter for green, and a filter for    blue in the adjacent pixel 5, and is effective also as one at 3    couples. It is effective also as one at 4 couples by adding the    filter for near-infrared rays. These 4 couples may be placed to the    matrix shape of 2×2. The color filter can also be formed by    multi-layering of a gelatin film, for example.    (Formation Process of Compound Semiconductor Thin Film of    Chalcopyrite Structure)

The compound semiconductor thin film of chalcopyrite structure whichfunctions as the optical absorption layer can be formed on thesemiconductor substrate or a glass substrate in which the circuit unit30 is formed by the vacuum evaporation method called the PVD (PhysicalVapor Deposition) method or the sputtering method. In this case, the PVDshall mean the method of forming a film by making the primary materialevaporated in the vacuum deposit.

When using the vacuum evaporation method, it is made to vapor-depositindependently on the substrate, in which the circuit unit 30 is formed,by making each component (Cu, In, Ga, Se) of the compound as a vacuumevaporation source.

In the sputtering method, a chalcopyrite compound is used as a target oreach of the components is independently used as a target.

In addition, since the substrate is heated to high temperature whenforming the compound semiconductor thin film of chalcopyrite structureon the glass substrate in which the circuit unit 30 is formed, thestoichiometry shift may occur by separation of a chalcogenide element.In this case, it is preferable by performing heat treatment for aboutone to several hours at the temperature of 400 to 600 degrees C. in thevapor phase atmosphere of Se or S after film formation in order tocompensate Se or S (a selenium processing or a sulfuric processing).

A formation process of the compound semiconductor thin film of thechalcopyrite structure applied to the solid state imaging deviceaccording to the first embodiment of the present invention is expressed,for example, as shown in FIG. 5.

When forming the CIGS thin film (Cu(In_(X), Ga_(1−X))Se₂ (where0<=X<=1)) of p⁻ type with which composition control is achieved, usingthe ion beam sputtering method, it is performed by dividing into threesteps, a stage I, a stage II, and a stage III, for example, as shown inFIG. 5. FIG. 5( a) shows ion species at the time of forming the film bythe ion beam sputtering method, and the substrate temperature in eachstage. FIG. 5( b) shows the composition ratio in each stage(Cu/(In+Ga)). The rate of In and Ga is suitably adjusted so that it maydescribe later. The substrate temperature is about 400 degrees C. alsothe highest, for example.

First of all, in the stage I, the composition ratio of (Cu/(In+Ga)) isremained 0, in a state where the group III element is a rich state.

Next, when shifting to the stage II, it shifts to the rich state of Cuelement of (Cu/(In+Ga)) whose composition ratio is 0 to not less than1.0.

Next, when shifting to the stage III, it shifts to the rich state of thegroup III element whose composition ratio is not more than 1.0 from therich state of Cu element whose composition ratio is not less than 1.0 of(Cu/(In+Ga)). Then, the compound semiconductor thin film (Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1)) of desired chalcopyrite structure isformed. As mentioned above, in this embodiment, the formation of thecompound semiconductor thin film 24 is performed in not more than about400 degrees C. When the substrate temperature is high enough, eachconstituent element may be diffused mutually.

FIG. 6 shows an SEM photograph (about 10,000 times) of a cross-sectionstructure of the photoelectric conversion unit formed by the fabricationmethod of the solid state imaging device according to the firstembodiment of the present invention. The lower electrode layer 25composed of Mo, the CIGS thin film 24 formed by patterning on the lowerelectrode layer 25, and the optical transparent electrode layer (ZnOfilm) 26 formed on the CIGS thin film 24 on the whole surface, areformed. In addition, although the buffer layer (CdS film) 36 intervenesbetween the CIGS thin film 24 and the optical transparent electrodelayer (ZnO film) 26 and is formed on the CIGS thin film 24 on the wholesurface, since the buffer layer (CdS film) 36 is very thin compared withother layers, it is not illustrated in FIG. 6. Moreover, although theinterlayer insulating film 34 exists in the same level as the CIGS thinfilm 24, it is not illustrated in FIG. 6.

(Energy Band Structure)

An energy band structure in the photoelectric conversion unit of thesolid state imaging device is expressed as schematically shown in FIG.7.

That is, FIG. 7( a) shows the energy band structure of the pn junctiondiode of the photoelectric conversion unit composed of ZnO (n)/CdS/CIGS(p) in a thermal equilibrium state when the composition of the CIGS thinfilm is formed uniform, and FIG. 7( b) shows the energy band structureof the pn junction diode of the photoelectric conversion unit composedof ZnO (n)/CdS/CIGS (p) in the thermal equilibrium state at the time ofcontrolling the composition of the CIGS thin film and performing bandgapcontrol. FIG. 7( c) shows a detailed enlarged drawing of the energy bandstructure of CIGS (p) thin film 24 part at the time of performingbandgap control of FIG. 7( b)

If the bandgap is large, the leakage current will be reduced and thedark current will decrease. On the other hand, if the bandgap is small,the photoelectric conversion efficiency will increase.

In the solid state imaging device, the composition control of the CIGSthin film in the photoelectric conversion unit is performed, the bandgapprofile is controlled, and thereby the reduction of dark current and theimprovement in the photoelectric conversion characteristic in apredetermined wavelength region can be achieved.

For example, as shown in FIG. 7( c), in order to reduce dark current,the composition of the compound semiconductor thin film (Cu(In_(x),Ga_(1−X))Se₂ (where 0<=X<=1)) 24 is made into Ga rich, and the energygaps E_(g1) and E_(g3) are enlarged so as to be illustrated, near the Moelectrode interface and near the pn junction interface.

On the other hand, in order to improve the photoelectric conversionefficiency in the near-infrared wavelength band region up to about 1300nm, the composition of the compound semiconductor thin film (Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1)) 24 is made into In rich in the range ofthe predetermined depth, and the energy gap E_(g2) is made small so asto be illustrated.

In addition, in the operation of the solid state imaging device, reversebias voltage is applied, for example, between the p type CIGS thin film24 and the n type optical transparent electrode layer (ZnO film) 26, andpixel information is detected.

FIG. 8 shows an example of an analysis result by AES (Auger ElectronSpectroscopy) of the compound semiconductor thin film (CIGS thin film)of the photoelectric conversion unit formed by the fabrication method ofthe solid state imaging device, and shows the relation between theatomic concentration (%) and the sputtering time.

The In rich region is formed in the predetermined depth in the compoundsemiconductor thin film (CIGS thin film) of the photoelectric conversionunit.

(Bandgap Energy and In/(In+Ga) Composition Ratio Characteristics)

The dependence of the bandgap energy of the compound semiconductor thinfilm (Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1)) of chalcopyrite structureapplied to the solid state imaging device and In/(In+Ga) compositionratio is expressed as shown in FIG. 9.

As shown in FIG. 9, the bandgap energy of Cu(Ga)Se₂ is 1.68 ev, thebandgap energy of Cu(In, Ga)Se₂ is 1.38 ev, and the bandgap energy ofCu(In)Se₂ is 1.04 ev.

Since the bandgap energy of the compound semiconductor thin film(Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1)) of chalcopyrite structure canbe made variable by controlling In/(In+Ga) composition ratio, as shownin FIG. 9, the photoelectric conversion wavelength can be made variableby the composition control.

(Photoelectric Conversion Characteristic)

The photoelectric conversion characteristic of the solid state imagingdevice is expressed as shown in FIG. 10. That is, in the wide wavelengthregion from the visible light wavelength region to the near infraredlight wavelength region, the photoelectric conversion characteristic ofhigh quantum efficiency is shown reflecting the quantum efficiency ofthe compound semiconductor thin film (Cu(In_(X), Ga_(1−X))Se₂ (where0<=X<=1)) 24 of chalcopyrite structure which functions as the opticalabsorption layer. Compared with the photoelectric conversioncharacteristic in the case of silicon (Si), the value of the quantumefficiency becomes two or more times.

The wavelength region is extensible to about 1300 nm which is awavelength of the near infrared light wavelength region by changing thecomposition of the compound semiconductor thin film (Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1)) 24 of chalcopyrite structure whichfunctions as the optical absorption layer from Cu(InGa)Se₂ to Cu(In)Se₂.

FIG. 11 shows the wavelength characteristic of the quantum efficiency ofthe compound semiconductor thin film (CIGS thin film) formed by thefabrication method of the solid state imaging device.

In the fabrication method of the solid state imaging device, the darkcurrent density of the same grade as the CIGS thin film formed at 550degrees C. is obtained by combining the composition control of thecompound semiconductor thin film (Cu(In_(X), Ga_(1−X)) Se₂ (where0<=X<=1)) 24, in a low temperature processing of 400 degrees C.

In the formation of the compound semiconductor thin film (Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1)), since the film formation by 550 degreesC. is general from a viewpoint of film quality and leakage current, itwas difficult to form semiconductor integrated circuits, such as CMOS,in a circuit unit. In contrast to it, in the solid state imaging device,low temperature processing by about 400 degrees C. becomes possible, andthe dark current is also suppressed, by formation of the compoundsemiconductor thin film (CIGS thin film) by composition control.

Moreover, also in the wavelength characteristic of the quantumefficiency of the compound semiconductor thin film (CIGS thin film)formed by the fabrication method of the solid state imaging device, thewavelength characteristic of the same grade as the CIGS thin film formedby 550 degrees C. is obtained, in the low temperature processing byabout 400 degrees C., by formation of the compound semiconductor thinfilm (CIGS thin film) by the composition control.

According to the optical absorption characteristics shown in FIG. 12,the penetration depth of the light which light intensity decreases to(1/e) can be obtained from the reciprocal of the absorption coefficient.Moreover, the energy gap of the corresponding compound semiconductorthin film (Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1)) 24 can be obtainedaccording to FIG. 9.

(Optical Absorption Characteristics)

The optical absorption characteristics of the solid state imaging deviceare expressed as shown in FIG. 12. That is, it has strong absorptionperformance reflecting the optical absorption coefficientcharacteristics of the compound semiconductor thin film (Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1)) 24 of chalcopyrite structure whichfunctions as the optical absorption layer, in the wide wavelength regionfrom visible light to a near infrared light wavelength region.

For example, it is about 100 times the absorption coefficient of silicon(Si) also in the visible light wavelength region, and the absorptionperformance is extensible to the wavelength of about 1300 nm by changingthe composition of the compound semiconductor thin film (Cu(In_(X),Ga_(1−X))Se₂ (where 0<=X<=1)) 24 of chalcopyrite structure whichfunctions as the optical absorption layer from CuGaSe₂ to CuInSe₂.

(Modified Example of First Embodiment)

As shown in FIG. 13 as a cross-sectional view of one pixel part, a solidstate imaging device according to amodified example of the firstembodiment of the present invention includes: a circuit unit 30 formedon the semiconductor substrate 10; and a photoelectric conversion unit28 including a lower electrode layer 25 placed on the circuit unit 30, acompound semiconductor thin film (Cu(In_(X), Ga_(1−X))Se₂ (where0<=X<=1)) 24 of chalcopyrite structure which is placed on the lowerelectrode layer 25 and functions as an optical absorption layer, and anoptical transparent electrode layer 26 placed on the compoundsemiconductor thin film 24.

The lower electrode layer 25, the compound semiconductor thin film 24,and the optical transparent electrode layer 26 are laminated one afteranother on the circuit unit 30.

Moreover, the circuit unit 30 includes a transistor by which the lowerelectrode layer 25 is connected to a gate electrode 16, in the solidstate imaging device.

As the lower electrode layer 25, molybdenum (Mo), niobium (Nb), tantalum(Ta), tungsten (W), etc. can be used, for example.

The optical transparent electrode layer 26 is composed of a non-dopedZnO film (i-ZnO) provided in an interface with the compoundsemiconductor thin film 24, and an n⁺ type ZnO film provided on thenon-doped ZnO film G-ZnO.

According to this configuration, the void and pinhole which are producedin the CIGS thin film of the underlying are embedded by asemi-insulating layer by providing a non-doped ZnO film (i-ZnO) as theoptical transparent electrode layer, and the CIGS thin film and i-pjunction is formed, and the generation of leakage current by the tunnelcurrent which occurs when a conductive ZnO film (n⁺) is contacted theCIGS thin film directly can be prevented. Therefore, the dark current atthe pn junction interface can be reduced by forming the non-doped ZnOfilm (i-ZnO) as a thick film.

Moreover, as the optical transparent electrode layer 26, other electrodematerials are also applicable. For example, an ITO film, a tin oxide(SnO₂) film, or an indium oxide (In₂O₃) film can be used.

In FIG. 13, the circuit unit 30 is formed with a CMOS integratedcircuit, for example. In FIG. 13, a gate insulating film placed on asemiconductor substrate 10 between source/drain regions 12 is omittingillustration. Moreover, a VIA electrode 32 embedded in an interlayerinsulating film 20 is placed between a gate electrode 16 and the lowerelectrode layer 25.

Moreover, as for the solid state imaging device according to themodified example of the first embodiment of the present invention, aphotoelectric conversion cell composed of the circuit unit 30 and thephotoelectric conversion unit 28 is integrated by one-dimensional matrixshape or two-dimensional matrix shape.

Moreover, in a plurality of integrated pixels, the optical transparentelectrode layer 26 is formed on the semiconductor substrate surface inone piece, and is performed in common electrically.

That is, in the solid state imaging device according to the firstembodiment of the present invention, the optical transparent electrodelayer 26 becomes a cathode electrode of the photo diode (PD) whichcomposes the photoelectric conversion unit 28, and is achieved byconstant potential (for example, power supply voltage). Therefore, in aplurality of integrated pixels, it is not necessary to perform isolationformation of the cathode electrode of the photo diode (PD) whichcomposes the photoelectric conversion unit 28, and it is formed on thesemiconductor substrate surface in one piece, and is performed in commonelectrically.

According to the solid state imaging device according to the modifiedexample of the 1st embodiment of the present invention, whole pixelregion of the photoelectric conversion cell is usable as the substantialphotoelectric conversion region by the laminated structure of thecircuit unit 30 and the photoelectric conversion unit 28. Accordingly,in the CMOS type image sensor, the optical aperture is about 80 to about90% compared with about 30 to about 40% of the optical aperture at thetime of forming in the semiconductor substrate by applying thephotoelectric conversion unit 28 as a pn junction diode, and it has alarge improvement effect.

According to the solid state imaging device according to the firstembodiment and its modified example of the present invention, the solidstate imaging device, with an easy structure, having the highsensitivity which reaches the wide wavelength region from visible lightto near infrared light wavelength region and reducing dark current canbe provided by providing the compound semiconductor film of thechalcopyrite structure composed of Cu(In, Ga)Se₂ in the photoelectricconversion unit.

Moreover, according to the fabrication method of the solid state imagingdevice according to the first embodiment and its modified example of thepresent invention, since the optical transparent electrode layer canform on the substrate surface in one piece and it does not need topattern the optical transparent electrode layer, the fabricating processcan be simplified.

Moreover, according to the solid state imaging device according to thefirst embodiment and its modified example of the present invention, thecarrier recombination processing can be reduced and the dark current canbe reduced by expanding the bandwidth using the CIGS based thin filmwhich replaced a part of In (indium) by gallium.

Moreover, according to the solid state imaging device according to thefirst embodiment and its modified example of the present invention, thedark current density can be reduced by the order of 10² by the bandgapcontrol by Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1).

[Second Embodiment]

(Element Structure)

A solid state imaging device according to a second embodiment of thepresent invention includes a circuit unit 30 formed on a substrate, anda photoelectric conversion unit 28 placed on the circuit unit 30, asshown in FIG. 14.

The photoelectric conversion unit 28 includes a compound semiconductorthin film (Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1)) 24 of chalcopyritestructure which functions as an optical absorption layer, and an opticaltransparent electrode layer 26 placed on the compound semiconductor thinfilm 24.

The optical transparent electrode layer 26 is composed of a non-dopedZnO film (i-ZnO) provided on an interface with the compoundsemiconductor thin film 24, and an n⁺ type ZnO film provided on thenon-doped ZnO film (i-ZnO).

According to this configuration, the void and pinhole which are producedin the CIGS thin film of the underlying are embedded by asemi-insulating layer by providing a non-doped ZnO film (i-ZnO) as theoptical transparent electrode layer, and the CIGS thin film and i-pjunction is formed, and the generation of leakage current by the tunnelcurrent which occurs when a conductive ZnO film (n⁺) is contacted theCIGS thin film directly can be prevented. Therefore, the dark current atthe pn junction interface can be reduced by forming the non-doped ZnOfilm (i-ZnO) as a thick film.

The circuit unit 30 is formed with a CMOS (Complementary Metal oxideSemiconductor Field Effect Transistor) integrated circuit etc., forexample. In FIG. 14, an n channel MOS transistor which composes a partof CMOS is shown in the circuit unit 30, and the circuit unit 30includes: a semiconductor substrate 10; source/drain regions 12 formedin the semiconductor substrate 10; a gate insulating film 14 placed onthe semiconductor substrate 10 between the source/drain regions 12; agate electrode 16 placed on the gate insulating film 14; a VIA0electrode 17 placed on the source/drain region 12, a wiring layer 18 forsource/drain placed on the VIA0 electrode 17, and a VIA1 electrode 23placed on the wiring layer 18. All of the VIA0 electrode 17, the wiringlayer 18, and the VIA1 electrode 23 are formed in an interlayerinsulating film 20.

A VIA electrode 33 placed on the source/drain region 12 is placed andformed of the VIA0 electrode 17, the wiring layer 18 placed on the VIA0electrode 17, and the VIA1 electrode 23 placed on the wiring layer 18.The VIA electrode 33 is shown also in the cross-section structure ofFIG. 15 described later.

In the solid state imaging device according to the second embodiment ofthe present invention, the source/drain region 12 of the n channel MOStransistor which compose a part of the CMOS and the photoelectricconversion unit 28 are electrically connected via the VIA electrode 33placed on the source/drain region 12.

Since the anode of the photo diode, which composes the photoelectricconversion unit 28, is connected to the source/drain region 12 of the nchannel MOS transistor, the optical information detected in the photodiode is switched by the n channel MOS transistor.

In addition, although the circuit unit 30 is shown by the example of thesemiconductor integrated circuit placed on the semiconductor substrate10 in the example of FIG. 14, the circuit unit 30 can also be formedwith the thin film transistor integrated circuit which integrates thethin film transistor formed on the thin film formed on the glasssubstrate, for example.

(Modified Example of Second Embodiment)

As shown in FIG. 15 as a cross-sectional view of one pixel part, a solidstate imaging device according to the modified example of the secondembodiment of the present invention includes: a circuit unit 30 formedon a semiconductor substrate 10; and a photoelectric conversion unit 28including a lower electrode layer 25 placed on the circuit unit 30, acompound semiconductor thin film (Cu(In_(X), Ga_(1−X))Se₂ (where0<=X<=1)) 24 of chalcopyrite structure which is placed on the lowerelectrode layer 25 and functions as an optical absorption layer, and anoptical transparent electrode layer 26 placed on the compoundsemiconductor thin film 24.

The lower electrode layer 25, the compound semiconductor thin film 24,and the optical transparent electrode layer 26 are laminated one afteranother on the circuit unit 30.

The circuit unit 30 includes a transistor by which the lower electrodelayer 25 is connected to the source/drain region 12, in the solid stateimaging device according to the modified example of the secondembodiment of the present invention.

As the lower electrode layer 25, molybdenum (Mo), niobium (Nb), tantalum(Ta), tungsten (W), etc. can be used, for example.

The optical transparent electrode layer 26 is composed of a non-dopedZnO film (i-ZnO) provided in an interface with the compoundsemiconductor thin film 24, and an n⁺ type ZnO film provided on thenon-doped ZnO film (i-ZnO).

According to this configuration, the void and pinhole which are producedin the CIGS thin film of the underlying are embedded by asemi-insulating layer by providing a non-doped ZnO film (i-ZnO) as theoptical transparent electrode layer, and the CIGS thin film and i-pjunction is formed, and the generation of leakage current by the tunnelcurrent which occurs when a conductive ZnO film (n⁺) is contacted theCIGS thin film directly can be prevented. Therefore, the dark current atthe pn junction interface can be reduced by forming the non-doped ZnOfilm (i-ZnO) as a thick film.

Furthermore, as the optical transparent electrode layer 26, otherelectrode materials are also applicable. For example, an ITO film, a tinoxide (SnO₂) film, or an indium oxide (In₂O₃) film can be used.

In FIG. 15, although the circuit unit 30 is formed with the CMOSintegrated circuit, for example, the details of the circuit omitexplanation. In FIG. 15, the gate insulating film 14 placed on thesemiconductor substrate 10 between the source/drain regions 12 isomitting illustration. Moreover, the VIA electrode 33 is placed betweenthe source/drain region 12 and the lower electrode layer 25.

Moreover, as for the solid state imaging device according to themodified example of the second embodiment of the present invention, thephotoelectric conversion cell composed of the circuit unit 30 and thephotoelectric conversion unit 28 is integrated by one-dimensional matrixshape or two-dimensional matrix shape.

In a plurality of pixels integrated by one-dimensional matrix shape ortwo-dimensional matrix shape, the optical transparent electrode layer 26is formed on the semiconductor substrate surface in one piece, and isperformed in common electrically.

That is, in the solid state imaging device according to the modifiedexample of the second embodiment of the present invention, the opticaltransparent electrode layer 26 becomes a cathode electrode of the photodiode (PD) which composes the photoelectric conversion unit 28, and isachieved by constant potential (for example, power supply voltage).Therefore, in a plurality of pixels integrated by one-dimensional matrixshape or two-dimensional matrix shape, it is not necessary to performisolation formation of the cathode electrode of the photo diode (PD)which composes the photoelectric conversion unit 28, and it is formed onthe semiconductor substrate surface in one piece, and should just beperformed in common electrically.

According to the solid state imaging device according to the modifiedexample of the second embodiment of the present invention, whole pixelregion of the photoelectric conversion cell is usable as the substantialphotoelectric conversion region by the lamination structure of thecircuit unit 30 and the photoelectric conversion unit 28. The opticalaperture is about 80 to 90%.

In the solid state imaging device according to the modified example ofthe second embodiment of the present invention, there is no amplifyingfunction for every pixel, compared with the first embodiment, reflectingthe difference in the circuit configuration.

On the other hand, since the configuration of the photoelectricconversion unit 28 is the same as that of the solid state imaging deviceaccording to the first embodiment, all of the formation processes of thecompound semiconductor thin film of the chalcopyrite structure shown inFIG. 5, the composition ratio dependence of the bandgap energy of thecompound semiconductor thin film shown in FIG. 9, the photoelectricconversion characteristic shown in FIG. 10, the wavelengthcharacteristic of the quantum efficiency of the compound semiconductorthin film (CIGS thin film) shown in FIG. 11, and the optical absorptioncharacteristics shown in FIG. 12, are the same also in the solid stateimaging device according to the second embodiment and its modifiedexample of the present invention. Moreover, the fabrication method afterformation of the circuit unit is common also about the fabricationmethod shown in FIG. 4. Therefore, these explanations are omitted.

According to the solid state imaging device according to the secondembodiment and its modified example of the present invention, the solidstate imaging device, with an easy structure, having the highsensitivity which reaches the wide wavelength region from visible lightto near infrared light wavelength region and reducing dark current canbe provided by providing the compound semiconductor film of thechalcopyrite structure composed of Cu(In, Ga)Se₂ in the photoelectricconversion unit.

Moreover, according to the fabrication method of the solid state imagingdevice according to the second embodiment and its modified example ofthe present invention, since the optical transparent electrode layer canform on the substrate surface in one piece and it does not need topattern the optical transparent electrode layer, the fabricating processcan be simplified.

Moreover, according to the solid state imaging device according to thesecond embodiment and its modified example of the present invention, thecarrier recombination processing can be reduced and the dark current canbe reduced by expanding the bandwidth using the CIGS based thin filmwhich replaced a part of In (indium) by gallium.

Moreover, according to the solid state imaging device according to thesecond embodiment and its modified example of the present invention, thedark current density can be reduced by the order of 10² by the bandgapcontrol by Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1).

[Other Embodiments]

The present invention has been described by the first to secondembodiments and its modification, as a disclosure including associateddescription and drawings to be construed as illustrative, notrestrictive. With the disclosure, artisan might easily think upalternative embodiments, embodiment examples, or application techniques.

Since the solid state imaging device according to the first to secondembodiment of the present invention has high sensitivity also in thenear infrared light wavelength region, the solid state imaging device isavailable enough as an image sensor for a security camera (camera whichperforms sensing of the visible light at daytime and performs sensing ofthe near infrared light wavelength region at night), and a personalauthentication camera (camera for performing personal authenticationwith the near infrared light wavelength region which is not affected byan influence of outdoor daylight) or an in-vehicle camera (cameramounted in a car for visual aid at night, distant visual field securing,etc.).

In the solid state imaging device according to the first to secondembodiment of the present invention, although Cu(In_(X), Ga_(1−X))Se₂(where 0<=X<=1) is used as the compound semiconductor thin film (CIGS)with chalcopyrite structure, it is not limited to this.

As the CIGS thin film, the thing of composition of Cu(In_(X), Ga_(1−X))(Se_(Y), S_(1−Y)) (where 0<=X<=1, 0<=Y<=1) is also known, and it isavailable also in the CIGS thin film with such composition.

As the compound semiconductor thin film of chalcopyrite structure, othercompound semiconductor thin films, such as CuAlS₂, CuAlSe₂, CuAlSe₂,CuAlTe₂, CuGaS₂, CuGaSe₂, CuGaTe₂, CuInS₂, CuInSe₂, CuInTe₂, AgAlS₂,AgAlSe₂, AgAlTe₂, AgGaS₂, AgGaSe₂, AgGaTe₂, AgInS₂, AgInSe₂, andAgInTe₂, are applicable.

In the solid state imaging device according to the first to secondembodiment of the present invention, a micro lens may be placed on eachpicture element region and thereby the collection efficiency for everypixel may be raised.

Moreover, although the embodiments having a plurality of pixels havebeen described, it may not limit to this and may compose as PD (photodiode) having only one light-receiving region, for example.

In the solid state imaging device according to the first to secondembodiment of the present invention, although the example which composesthe CMOS integrated circuit formed on the semiconductor substrate ismainly described about the circuit unit 30, the circuit unit 30 is notlimited to the CMOS and other circuit configurations may be used for thecircuit unit 30. For example, the compound semiconductor thin film ofthe chalcopyrite structure applied with the solid state imaging deviceaccording to the first to second embodiment of the present invention maybe used for the photoelectric conversion unit 28, and a charge transferfunction may be given to the circuit unit as well as CCD (Charge CoupledDevice).

In the solid state imaging device according to the first to secondembodiment of the present invention, although the semiconductorsubstrate is mainly explained about the substrate, a thin film may beformed on a glass substrate and the predetermined circuit unit composedof a thin film transistor may be formed on the aforementioned thin film,as an easy configuration.

In the solid state imaging device according to the first to secondembodiment and its modified example of the present invention, althoughthe example of the semiconductor is mainly described about thesubstrate, it does not limit to a mono-crystal substrate as thesubstrate. A SOI (Silicon On Insulator) substrate may be used for thepurpose of low power consumption and improvement in the speed.

Such being the case, the present invention covers a variety ofembodiments, whether described or not. Therefore, the technical scope ofthe present invention is appointed only by the invention specific matterrelated appropriate scope of claims from the above-mentionedexplanation.

According to the solid state imaging device of the present invention,the solid state imaging device, with an easy structure, having the highsensitivity which reaches the wide wavelength region from visible lightto near infrared light wavelength region and reducing dark current canbe provided by providing the compound semiconductor film of thechalcopyrite structure in the photoelectric conversion unit.

Moreover, according to the fabrication method of the solid state imagingdevice of the present invention, since the optical transparent electrodelayer can form on the substrate surface in one piece and it does notneed to pattern the optical transparent electrode layer, the fabricatingprocess can be simplified.

Moreover, according to the solid state imaging device of the presentinvention, the carrier recombination processing can be reduced and thedark current can be reduced by expanding the bandwidth using the CIGSbased thin film composed of Cu(In, Ga)Se₂ which replaced a part of In(indium) by gallium.

Moreover, according to the solid state imaging device of the presentinvention, the dark current density can be reduced by the order of 10²by the bandgap control by Cu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1).

INDUSTRIAL APPLICABILITY

Since the solid state imaging device according to the embodiments of theinvention has high sensitivity also in a near infrared light wavelengthregion, it is available enough as the image sensor for a security camera(camera which performs sensing of the visible light at daytime andperforms sensing of the near infrared light wavelength region at night),personal authentication camera (camera for performing personalauthentication with the near infrared light wavelength region which isnot affected by an influence of outdoor daylight) or in-vehicle camera(camera mounted in a car for visual aid at night, distant visual fieldsecuring, etc.), and also an image sensor for near infrared lightwavelength region detection of medical application.

1. A solid state imaging device comprising: a circuit unit formed on asubstrate; and a photoelectric conversion unit including a lowerelectrode layer placed on the circuit unit, a compound semiconductorthin film of chalcopyrite structure which is placed on the lowerelectrode layer and functions as an optical absorption layer, and anoptical transparent electrode layer placed on the compound semiconductorthin film, wherein the lower electrode layer, the compound semiconductorthin film, and the optical transparent electrode layer are laminated oneafter another on the circuit unit, and wherein the compoundsemiconductor thin film includes a first region and a second regionsequentially in a direction from the optical transparent electrode layertoward the substrate, atomic concentration of Ga in the first region ishigher than atomic concentration of In in the first region, and atomicconcentration of Ga in the second region is lower than atomicconcentration of In in the second region.
 2. The solid state imagingdevice according to claim 1, wherein the circuit unit includes atransistor by which the lower electrode layer is connected to a gate. 3.The solid state imaging device according to claim 1, wherein the circuitunit includes a transistor by which the lower electrode layer isconnected to a source or a drain.
 4. The solid state imaging deviceaccording to claim 1, wherein the circuit unit and a photoelectricconversion cell composed of the photoelectric conversion unit areintegrated.
 5. The solid state imaging device according to claim 1,wherein the circuit unit and a photoelectric conversion cell composed ofthe photoelectric conversion unit are integrated, and the opticaltransparent electrode layer is formed on a substrate surface in onepiece.
 6. The solid state imaging device according to claim 1, whereinthe compound semiconductor thin film of the chalcopyrite structure isCu(In_(X), Ga_(1−X))Se₂ (where 0<=X<=1).
 7. The solid state imagingdevice according to claim 1, wherein the optical transparent electrodelayer includes a non-doped ZnO film provided on an interface with thecompound semiconductor thin film, and an n type ZnO film provided on thenon-doped ZnO film.
 8. The solid state imaging device according to claim1, wherein the solid state imaging device is photo sensor havingsensitivity also in a near infrared optical wavelength region.
 9. Thesolid state imaging device according to claim 1, wherein the solid stateimaging device includes a color filter on the optical transparentelectrode layer.